The use of an insulating layer for altering the junction forming characteristics of semiconductor materials is well known in the art of crystalline semiconductors such as single crystal silicon. A thin insulating oxide layer is generally interposed between semiconductor materials to alter the surface state of the adjoining materials, modifying the electronic band bending and the associated space charge distribution of the semiconductor junction. Typically, the oxide layer is either grown from the surface of the semiconductor or deposited onto the semiconductor from an extrinsic source. The term "grown" collectively represents the varied techniques for oxidizing the surface region of the semiconductor material. In specialized electronic applications, the thickness of the oxide layer is limited to below about 50 Angstroms. The thin oxide layer is sufficient to alter the material's surface states yet concurrently permit substantial conduction by tunneling means for an appropriately baised device. The term tunneling, as used herein and known to those of the art, refers to the ability of charge carriers to pass through a narrow junction region to allowable energy levels on the far side of the junction even though these charge carriers have insufficient energy to surmount the barrier formed at the MIS junction. In other applications thicker oxide layers have been used in field effect devices and the like.
In general, the controlled growth or deposition of insulating oxide layers on semiconductor materials such as single crystal silicon has greatly extended semiconductor technology.
The present invention teaches a technique for controlled chemical growth of an oxide layer onto a relatively new semiconductor material photoconductive amorphous silicon. Amorphous silicon MIS devices, as detailed herein, not only benefit from the junction modifying characteristics of the insulator interface, but also demonstrate a substantially increased stability of electronic properties.